There are numerous applications for imaging sensors that provide infrared search and track (IRST), targeting or standoff reconnaissance functions, such as on an aircraft including an unmanned aerial vehicle (UAV) platform for standoff reconnaissance or on a jet aircraft for IRST, targeting (i.e., target location and designation) and standoff reconnaissance (e.g., survey or observation to collect image information). Additionally, some IRST systems include laser range-finding, and/or coherent laser detection and ranging (LADAR) capabilities. As its name indicates, an IRST system operates generally in the infrared wavelength range; however visible and short wave infrared (SWIR) wavelength sensing capability may also be desired within the IRST sensor.
Sensors to be used on aircraft are typically mounted within a pod that is mounted to the aircraft, and as a result are constrained to fit within the volume of the pod. Traditional pod-mounted electro-optic infrared sensors used solely for targeting functions usually have aperture*FOV (field of view) products, for the elevation axis, in the range of about 4-5 inch-degrees. Certain multi-function airborne sensor systems that include IRST capability, such as that disclosed in U.S. Pat. No. 8,759,735, for example, have extended the range of the elevation aperture*FOV product to about 10-12 inch-degrees. Some attempts to further increase the elevation field of view, and therefore the elevation aperture*FOV product, have involved the use of refractive optics; however, these attempts have not enjoyed great success, and severely limit the sensor capabilities due to spectral bandwidth limitations associated with refractive optical elements.